This invention relates to a knee brace and particularly to a knee brace applied to a patient's knee subsequent a fracture of tibia or femur, or after operation on the knee or in other cases where knee flexion and extension is desired under a restricted and/or supported condition.
It has been found that the traditional immobilization of joints above and below a fractured bone results in undesirable consequences to the joints. While temporary stiffness of the immobilized joint and atrophy of the limb musculature are recognized as an inevitable consequence of such practice, often iatrogenic stiffness and swelling can constitute a severe complication and should be avoided if possible.
It has been discovered that the use of a brace at the site of the knee to allow a degree of motion to the knee joint while providing a connective support between the tibia and femur will substantially reduce the expected joint stiffness and muscle atrophy and will curtail pain and swelling that often accompanied removal of conventional casts which immobilized joints.
Because the knee is not a single-axis joint, the use of a bracing system with a single pivot axis caused pistoning of the leg and either failed to provide the support necessary or caused additional trauma prolonging recovery. Bracing devices employing more than one axis were developed in an attempt to follow the polycentric movement of the knee joint. Most prior art devices employ members with a gear tooth interconnection where two elongated elements each have a gear tooth end and proximately spaced pivotal axis pins interconnected by a connecting link. However, either because the true motion of the knee joint was not correctly understood or for reasons of simplicity, the devices devised did not follow the kinematic motion of the knee and the resultant motion for each element was essentially symmetrical or mirror-like in effect.
One prior art device employed a four-bar link concept which, however, was arranged in a symmetrical manner and essentially duplicated, with some enlargement, the mirror-like motion path common to the gear-type mechanisms.
In the authoritative publication, "Kinematics of the Human Knee Joint", IBM New York Scientific Center Report No. 320-2928, January 1968, the precise motion of the polycentric knee joint was described and defined. Computer aided synthesis was employed by Applicant to duplicate this motion in a mechanism. While exact duplication required mechanics of awkward design, the motion could be closely followed within practical limits by a four-bar linkage with assymetrical positioning of its linkage axes. The resultant motion did not have the mirror-image effect of prior art systems, but parodied the assymetrical motion of the human knee.